The invention relates generally to switching devices that use liquid crystals. More particularly, the invention relates to switching devices prepared from polymers or self-assembled monolayers containing redox-active groups that induce a shift in the orientation of liquid crystals when the oxidation state of the redox-active group is altered.
Various display devices are known in the art. The prior art devices generally require a relatively high voltage or a relatively high current. Because power (Watts) is determined by multiplying current (Amps) by voltage (Volts), P=I*V, such devices generally require relatively high power to operate. For example electrochromic displays exist that have a low switching potential but require a high current. Such devices typically consume too much power to be useful in portable devices. On the other hand, conventional displays use low currents but require high applied potentials such that power consumption is still too high for many applications.
Although suitable switching mechanisms exist, a need remains for switching mechanisms which operate at low power and moderate response times. These types of switching mechanisms might find use in applications such as electronic labels, electronic ink, or electronic paper. There is also substantial interest in finding ways to switch the orientations of liquid crystals using driving circuitry that can be easily fabricated.
The present invention provides liquid crystal devices in which the orientation of the liquid crystal is altered when the oxidation state of a redox-active group is changed. The invention further provides methods for producing liquid crystal devices, methods for changing the orientation of a liquid crystal, and kits for producing liquid crystal devices.
A liquid crystal switching device includes a first substrate having a first surface; a redox-active material disposed on at least a first portion of the first surface, the redox-active material comprising at least one redox-active group; a liquid crystal disposed above the top of the redox-active material; and a salt dispersed in the liquid crystal. When the oxidation state of the redox-active groups are changed from a first oxidation state to a second oxidation state, such as by electrochemical oxidation, electrochemical oxidation using a redox mediator species, or oxidation using a chemical oxidizing agent, the liquid crystal changes its orientation with respect to the first surface of the first substrate providing a detectable change in the appearance of the liquid crystal.
In some embodiments of the invention, the first surface of the first substrate, or at least one region of the first surface, is electrically conducting. Further liquid crystal devices are provided in which the electrically conducting surface or surface region is a metallized top surface or surface region. Further liquid crystal devices are provided in which the metallized top surface or surface region of the first substrate comprises a metal selected from gold, silver, copper, nickel, palladium, platinum, or combinations thereof. In embodiments where the first surface comprises at least one electrically conducting region, the redox-active material is disposed on at least a portion of the electrically conducting region.
In other provided devices, the redox-active groups are supported on electrically conducting surfaces or surface regions, other than a metallized surfaces or surface regions, such as surfaces or surface regions made from conducting organic materials such as polymers or conducting metal oxides, such as indium tin oxide (ITO) or titanium dioxide. ITO is a substrate in some provided devices because it is optically transparent. Conducting polymers are substrates in other provided devices and may be flexible.
Still other liquid crystal devices are provided in which the metallized top surface or surface region is gold. In some provided liquid crystal devices, the gold is uniformly deposited without any overall azimuthal preference whereas in other devices, the gold or other metal is obliquely deposited. In some provided devices, the gold is obliquely deposited at an angle of from 35xc2x0 to 60xc2x0 whereas in other devices the gold is deposited at an angle of at or about 40xc2x0. The angle is defined as the angle from the normal of the substrate.
Liquid crystal devices are further provided in which the surface-bound redox-active group is selected from a group that includes ferrocene; a derivatized ferrocene such as nonamethyl ferrocene; a viologen; a pyridine, bipyridine or salts of these; a metal meso porphyrin; a quinone; a hydroquinone; an anthracene and other monocyclic and polycyclic aromatic compounds; or combinations thereof. Still other liquid crystal devices are provided in which the surface-bound redox-active groups attached to a metallized surface or metallized surface region of a first substrate are formed by reacting a compound of formula Fcxe2x80x94(CH2)nxe2x80x94SH with the first surface or surface region forming a self-assembled monolayer (SAM) where Fc is ferrocene and n has a value ranging from 1 to 20, 3 to 18, 5 to 15, 6 to 14, 8 to 12, 9 to 11, 10, or 11.
Further liquid crystal devices are provided in which surface-bound redox-active groups are attached to one portion of the surface of the substrate and another portion of the surface of the substrate does not contain any of the surface-bound redox-active groups. In still other provided devices, the region of the surface of the substrate with surface-bound redox-active groups has a defined shape such as a number, letter, symbol, circle, triangle, square, pentagon or other polygon.
Other liquid crystal devices are provided in which the surface-bound redox-active groups attached to the surface of the substrate are redox-active groups of a polymer coated on the surface of the substrate. In further provided liquid crystal devices, the redox-active groups of the polymer are ferrocene groups whereas in yet other such devices the polymer is poly(vinylferrocene) or a polymer that incorporates at least some vinylferrocene.
Further liquid crystal devices are provided in which the liquid crystal is a nematic liquid crystal. Still other devices are provided in which the liquid crystal has a dipole moment that is parallel to the long axis of the liquid crystal. Yet other liquid crystal devices are provided in which the liquid crystal is 4-cyano-4xe2x80x2-pentylbiphenyl (5CB). Still other devices are provided in which the liquid crystal is either a cholesteric phase or a smectic phase, including ferroelectric phases (smectic C*).
Yet other liquid crystal devices are provided in which the salt of the device is a tetraalkylammonium salt. In some provided devices, the salt is a tetraalkylammonium tetrafluoroborate, a tetraalkylammonium hexafluorophosphate, or a tetraalkylammonium tetraphenylborate. In other provided devices, the salt is a tetraalkylammonium tetrafluoroborate or a 1-alkyl-4-alkylcarbamoyl-pyridinium tetrafluoroborate. In still other provided devices, the salt is a tetrabutylammonium salt such as tetrabutylammonium tetrafluoroborate. In other devices, the salt is a metal halide, such as, but not limited to, sodium bromide. In other devices, the salts are organic-inorganic hybrids involving organic encapsulated metals such as dicyclohexyl 18-crown-6 potassium tetrafluoroborate (18C-6/KBF4), 15-crown-5 sodium tetraphenyl borate (15C-5/NaO4B) or cryptofix-2-2-2 potassium tetrafluoroborate (K*/BF4).
In still other provided liquid crystal devices, the salt is dispersed in the liquid crystal at a concentration of from 1 xcexcM to 80 mM assuming perfect dissolution. In still other provided devices, the salt is dispersed in the liquid crystal at a concentration of from 5 mM to 75 mM, of from 10 mM to 60 mM, of from 15 mM to 50 mM, of from 20 mM to 40 mM, of from 25 mM to 40 mM, of from 30 mM to 35 mM, or of about 35 mM.
Other liquid crystal devices are further provided in which the liquid crystal is oriented planar to the surface of the substrate when the redox-active group is in a reduced state and is oriented perpendicular to the surface of the substrate when the redox-active group is in an oxidized state.
Still other liquid crystal devices are provided in which the redox-active group of the device is oxidized using an oxidizing agent. In some provided devices, the oxidizing agent is a peroxide such as benzoyl peroxide.
Still other liquid crystal devices are provided in which the redox-active group is oxidized by applying a potential to the substrate or electrically conducting surface or surface region of the substrate.
Still further liquid crystal devices are provided which include a redox mediator, and the redox-active group is oxidized by interaction with the redox mediator. In some such provided devices, the redox mediator is dispersed within the liquid crystal and in still other such devices the redox mediator is selected from free ferrocene, pyridine compounds, bipyridine compounds, and metal ions such as Co+2 and Co+3.
Other liquid crystal devices are provided in which the substrate is selected from a metal, a polymer, or a silica material such as glass or quartz. In some provided liquid crystal devices, the substrate is a metal substrate and the top surface of the substrate provides a metallized surface. In other provided liquid crystals, the metallized top surface is a metal deposited on glass or quartz.
Further liquid crystal devices are provided that include a second substrate having a second surface. The second substrate overlies the first substrate defining a space between the top of the redox-active material and the second substrate, and the liquid crystal and salt are located in the defined space, forming an electrooptical cell. Some such liquid crystal devices are provided which further include a spacing material separating the first substrate from the second substrate. In certain provided devices, the spacing material is a polymeric film such as Mylar(copyright) brand film whereas in other provided devices, the spacing material is microspheres. Still other liquid crystal devices are provided in which the first surface of the first substrate or second surface of the second substrate is connected to a power supply and an electrical potential supplied by the power supply oxidizes the redox-active group bound to the first surface of the first substrate.
In some liquid crystal devices that include a second substrate have a second electrically conductive surface or surface region, the conductive material of the second surface or surface region includes a metal and in some such devices the included metal is selected from gold, silver, copper, nickel, palladium, platinum, or combinations of these metals. In some provided devices, the conductive material is a conducting polymer or conducting metal oxide as described above.
In some liquid crystal devices both the first and second substrates have at least one metallized surface or surface region made from the same metal. In some such provided devices, the second metallized surface or surface region is made from a metal without any azimuthal preference (does not cause a liquid crystal to assume any preferred, overall azimuthal orientation) whereas in other provided devices the metallized second surface or surface region of the second faces the liquid crystal and comprises an obliquely deposited metal such as those having the characteristics described above with respect to the first substrate. In some such provided devices, the first surface of the first substrate has a metallized surface or at least one metallized region having an obliquely deposited metal such as gold deposited thereon, and the second surface or surface region of the second substrate is an obliquely deposited metal such as gold. In some such devices, the direction of deposition of the metal for the second surface of the second substrate and the metallized surface of the first substrate is the same.
A liquid crystal electrooptical cell is further provided. The liquid crystal electrooptical cell includes a working electrode comprising a conductive material and a redox layer comprising redox-active molecules disposed on at least a portion of the working electrode, each of the redox-active molecules comprising at least one redox-active group; a counter electrode comprising a conductive material; a liquid crystal; and a salt. The working electrode and the counter electrode define a space at least partially filled with the liquid crystal, and the salt is dispersed in the liquid crystal. The redox-active material disposed on the surface of the working electrode contacts the liquid crystal in the space between the working and counter electrodes.
A liquid crystal electrooptical cell is further provided in which the liquid crystal and the salt have any of the characteristics described above.
Some liquid crystal electrooptical cells are provided in which the redox-active group is a pendant group of a polymer coated on the surface of the working electrode whereas in other provided cells, the redox-active group is present on a thiol that forms a self-assembled monolayer on the surface of the working electrode. In still other provided such cells, the polymer coated on the surface of the working electrode is a poly(vinylferrocene) or a polymer formed from vinylferrocene, and ferrocene is the redox-active group. In still other provided such cells, the self-assembled monolayer is formed from a ferrocenylalkanethiol having the formula Fcxe2x80x94(CH2)nxe2x80x94SH where Fc is ferrocene and n has any of the values described above.
Liquid crystal electrooptical cells are further provided which include a spacer material such as a film or microspheres that separates the working electrode from the counter electrode. Yet other liquid crystal electrooptical cells are provided in which the liquid crystal further includes a redox mediator having any of the characteristics described above.
Still other liquid crystal electrooptical cells are provided in which the working electrode is a metallized top surface or surface region of a substrate. In yet other such cells, the metallized top surface or surface region of the substrate and the substrate have any of the characteristics described above.
Still other liquid crystal electrooptical cells are provided in which the counter electrode is a metal having any of the characteristics described above, and other liquid crystal electrooptical cells are provided in which the counter electrode has any of the features of the second substrate described above. Yet other liquid crystal electrooptical cells are provided in which the redox-active material disposed on at least one portion of a surface of the first electrode is disposed on a portion having a defined shape as described above.
In one embodiment, the invention provides a liquid crystal electrooptical cell. The electrooptical cell includes a working electrode comprising a glass slide support having an obliquely deposited gold top surface and a self-assembled monolayer formed by contacting a ferrocenylalkanethiol with the obliquely deposited gold top surface, wherein the ferrocenyl alkanethiol has the structure Fcxe2x80x94(CH2)nxe2x80x94SH, wherein Fc is ferrocene and n is an integer having a value from 10 to 12. The electrooptical cell also includes a counter electrode comprising a gold surface positioned at least 25 xcexcm away from the obliquely deposited gold top surface of the working electrode defining a space between the gold surface of the counter electrode and the obliquely deposited gold top surface of the working electrode. The obliquely deposited gold top surface of the working electrode faces the gold surface of the counter electrode, and the obliquely deposited gold top surface of the working electrode and the gold surface of the counter electrode are positioned such that the surfaces are parallel to one another. A doped liquid crystal fills at least a portion of the space defined by the gold surface of the counter electrode and the obliquely deposited gold top surface of the working electrode. In some such embodiments, the doped liquid crystal comprising 4-cyano-4xe2x80x2-pentylbiphenyl and tetrabutylammonium tetrafluoroborate.
In A method of manufacturing a liquid crystal device is further provided. The method includes depositing a material having one or more redox-active groups on at least a portion of a surface of a substrate material, disposing a liquid crystal over the material having the redox-active groups; and dispersing a salt in the liquid crystal.
Further methods are provided in which the salt is dispersed in the liquid crystal before the liquid crystal is disposed over the material having the redox-active groups. In the provided methods, the liquid crystal and the salt have any of the features described above.
Further methods are provided which include positioning a second substrate over the surface of the first substrate on which the redox-active groups have been deposited. In yet other provided methods, a spacing material is positioned over the surface of the first substrate material on which the material with the redox-active group has been deposited and then the second substrate material is placed over the spacing material. In still other provided methods the substrate on which the material with the redox-active group has been deposited and the second substrate are both planar and spaced apart in a parallel fashion. In still other provided methods, the surface of a planar conductive material on which a material with a redox-active group has been deposited is positioned less than or about 25 xcexcm from a nearest surface of a second planar conducting material. In the provided methods, the first and second substrates have any of the features described above.
Further methods are provided which include depositing the redox-active material over at least a portion of the surface of a substrate where the surface and the substrate have any of the features described above. In still other provided methods, the material with the redox-active groups is coated on the surface of the substrate. In yet other provided methods, the material coated on the surface of the substrate is a polymer that includes the redox-active groups. In still other provided methods, the polymer has pendant ferrocene groups such as polymers formed from vinylferrocene such as poly(vinylferrocene) and other polymers that incorporate vinylferrocene.
A method of changing the orientation of a liquid crystal is further provided. The method includes oxidizing or reducing the redox-active group of any of the liquid crystal devices or cells described above. In some provided such methods, the redox-active group is oxidized with a chemical oxidizing agent. In some such provided methods, the chemical oxidizing agent is a peroxide and in other provided methods the chemical oxidizing agent is benzoyl peroxide.
Other methods for changing the orientation of a liquid crystal are provided in which the redox-active group is oxidized or reduced by applying a potential to an electrically conducting surface such as the metallized top surface or surface region of the first substrate of some embodiments, or the conductive material of the second substrate. In other provided methods, the orientation of the liquid crystal is changed by applying a potential to the working or counter electrode of a liquid crystal electrooptical cell, thereby oxidizing or reducing the redox-active group. In some provided methods, a potential of less than +350 mV is sufficient to oxidize the redox-active group. In other provided methods, a potential of less than +250 mV is sufficient to oxidize the redox-active group. In still other provided methods, a potential of less than +200 mV, less than +100 mV, or less than +50 mV is sufficient to oxidize the redox-active group.
A kit for manufacturing a liquid crystal device is further provided. The kit includes a substrate having a surface having any of the features described above; a material with a redox-active group having any of the features described above; a liquid crystal having any of the features described above; and a salt having any of the features described above. Some provided kits further include instructions for assembling a liquid crystal device or cell.
Further kits are provided which include a second substrate or a second electrode having any of the features described above.
Further kits are provided which further include a spacing material having the features described above for use in spacing a first substrate from a second substrate or a first electrode from a second electrode.
In some provided kits, the material with the redox-active group is disposed on a surface of the substrate whereas in other provided kits, the instructions describe how the material with the redox-active group is placed on the surface of the substrate.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.